/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.runners.gaia.translation.wrappers.streaming.stableinput;



import com.bff.gaia.unified.runners.core.DoFnRunner;

import com.bff.gaia.unified.runners.gaia.translation.types.CoderTypeSerializer;

import com.bff.gaia.unified.sdk.state.TimeDomain;

import com.bff.gaia.unified.sdk.coders.Coder;

import com.bff.gaia.unified.sdk.transforms.DoFn;

import com.bff.gaia.unified.sdk.transforms.windowing.BoundedWindow;

import com.bff.gaia.unified.sdk.util.WindowedValue;

import com.bff.gaia.api.common.state.ListState;

import com.bff.gaia.api.common.state.ListStateDescriptor;

import com.bff.gaia.runtime.state.KeyedStateBackend;

import com.bff.gaia.runtime.state.OperatorStateBackend;

import org.joda.time.Instant;



import javax.annotation.Nullable;

import java.util.*;



/**

 * A {@link DoFnRunner} which buffers data for supporting {@link

 * DoFn.RequiresStableInput}.

 *

 * <p>When a DoFn is annotated with @RequiresStableInput we are only allowed to process elements

 * after a checkpoint has completed. This ensures that the input is stable and we produce idempotent

 * results on failures.

 */

public class BufferingDoFnRunner<InputT, OutputT> implements DoFnRunner<InputT, OutputT> {



  public static <InputT, OutputT> BufferingDoFnRunner<InputT, OutputT> create(

      DoFnRunner<InputT, OutputT> doFnRunner,

      String stateName,

      Coder windowedInputCoder,

      Coder windowCoder,

      OperatorStateBackend operatorStateBackend,

      @Nullable KeyedStateBackend<Object> keyedStateBackend)

      throws Exception {

    return new BufferingDoFnRunner<>(

        doFnRunner,

        stateName,

        windowedInputCoder,

        windowCoder,

        operatorStateBackend,

        keyedStateBackend);

  }



  /** The underlying DoFnRunner that any buffered data will be handed over to eventually. */

  private final DoFnRunner<InputT, OutputT> underlying;

  /** A union list state which contains all to-be-acknowledged snapshot ids. */

  private final ListState<CheckpointElement> notYetAcknowledgedSnapshots;

  /** A factory for constructing new BufferingElementsHandler scoped by an internal id. */

  private final BufferingElementsHandlerFactory bufferingElementsHandlerFactory;



  /** The current active state id which is later linked to a checkpoint id. */

  private String currentStateId;

  /** The current handler used for buffering. */

  private BufferingElementsHandler currentBufferingElementsHandler;



  private BufferingDoFnRunner(

      DoFnRunner<InputT, OutputT> underlying,

      String stateName,

      Coder inputCoder,

      Coder windowCoder,

      OperatorStateBackend operatorStateBackend,

      @Nullable KeyedStateBackend keyedStateBackend)

      throws Exception {



    this.underlying = underlying;

    this.notYetAcknowledgedSnapshots =

        operatorStateBackend.getUnionListState(

            new ListStateDescriptor<>("notYetAcknowledgedSnapshots", CheckpointElement.class));

    this.bufferingElementsHandlerFactory =

        (stateId) -> {

          ListStateDescriptor<BufferedElement> stateDescriptor =

              new ListStateDescriptor<>(

                  stateName + stateId,

                  new CoderTypeSerializer<>(new BufferedElements.Coder(inputCoder, windowCoder)));

          if (keyedStateBackend != null) {

            return KeyedBufferingElementsHandler.create(keyedStateBackend, stateDescriptor);

          } else {

            return NonKeyedBufferingElementsHandler.create(

                operatorStateBackend.getListState(stateDescriptor));

          }

        };

    this.currentStateId = generateNewId();

    this.currentBufferingElementsHandler = bufferingElementsHandlerFactory.get(currentStateId);

  }



  @Override

  public void startBundle() {

    // Do not start a bundle, start it later when emitting elements

  }



  @Override

  public void processElement(WindowedValue<InputT> elem) {

    currentBufferingElementsHandler.buffer(new BufferedElements.Element(elem));

  }



  @Override

  public void onTimer(

      String timerId, BoundedWindow window, Instant timestamp, TimeDomain timeDomain) {

    currentBufferingElementsHandler.buffer(

        new BufferedElements.Timer(timerId, window, timestamp, timeDomain));

  }



  @Override

  public void finishBundle() {

    // Do not finish a bundle, finish it later when emitting elements

  }



  @Override

  public DoFn<InputT, OutputT> getFn() {

    return underlying.getFn();

  }



  /** Should be called when a checkpoint is created. */

  public void checkpoint(long checkpointId) throws Exception {

    // We are about to get checkpointed. The elements buffered thus far

    // have to be added to the global CheckpointElement state which will

    // be used to emit elements later when this checkpoint is acknowledged.

    addToBeAcknowledgedCheckpoint(checkpointId, currentStateId);

    currentStateId = generateNewId();

    currentBufferingElementsHandler = bufferingElementsHandlerFactory.get(currentStateId);

  }



  /** Should be called when a checkpoint is completed. */

  public void checkpointCompleted(long checkpointId) throws Exception {

    List<CheckpointElement> toAck = removeToBeAcknowledgedCheckpoints(checkpointId);

    for (CheckpointElement toBeAcked : toAck) {

      BufferingElementsHandler bufferingElementsHandler =

          bufferingElementsHandlerFactory.get(toBeAcked.internalId);

      Iterator<BufferedElement> iterator = bufferingElementsHandler.getElements().iterator();

      boolean hasElements = iterator.hasNext();

      if (hasElements) {

        underlying.startBundle();

      }

      while (iterator.hasNext()) {

        BufferedElement bufferedElement = iterator.next();

        bufferedElement.processWith(underlying);

      }

      if (hasElements) {

        underlying.finishBundle();

      }

      bufferingElementsHandler.clear();

    }

  }



  private void addToBeAcknowledgedCheckpoint(long checkpointId, String internalId)

      throws Exception {

    notYetAcknowledgedSnapshots.addAll(

        Collections.singletonList(new CheckpointElement(internalId, checkpointId)));

  }



  private List<CheckpointElement> removeToBeAcknowledgedCheckpoints(long checkpointId)

      throws Exception {

    List<CheckpointElement> toBeAcknowledged = new ArrayList<>();

    List<CheckpointElement> checkpoints = new ArrayList<>();

    for (CheckpointElement element : notYetAcknowledgedSnapshots.get()) {

      if (element.checkpointId <= checkpointId) {

        toBeAcknowledged.add(element);

      } else {

        checkpoints.add(element);

      }

    }

    notYetAcknowledgedSnapshots.update(checkpoints);

    // Sort by checkpoint id to preserve order

    toBeAcknowledged.sort(Comparator.comparingLong(o -> o.checkpointId));

    return toBeAcknowledged;

  }



  private static String generateNewId() {

    return UUID.randomUUID().toString();

  }



  /** Constructs a new instance of BufferingElementsHandler with a provided state namespace. */

  private interface BufferingElementsHandlerFactory {

    BufferingElementsHandler get(String stateId) throws Exception;

  }



  private static class CheckpointElement {



    final String internalId;

    final long checkpointId;



    CheckpointElement(String internalId, long checkpointId) {

      this.internalId = internalId;

      this.checkpointId = checkpointId;

    }

  }

}